Coke is a solid carbon fuel and carbon source used to melt and reduce iron ore in the production of steel. In one process, known as the “Thompson Coking Process,” coke is produced by batch feeding pulverized coal to an oven that is sealed and heated to very high temperatures for approximately forty-eight hours under closely-controlled atmospheric conditions. Coking ovens have been used for many years to convert coal into metallurgical coke. During the coking process, finely crushed coal is heated under controlled temperature conditions to devolatilize the coal and form a fused mass of coke having a predetermined porosity and strength. Because the production of coke is a batch process, multiple coke ovens are operated simultaneously.
Much of the coke manufacturing process is automated due to the extreme temperatures involved. For example, a pusher charger machine (“PCM”) is typically used on the coal side of the oven for a number of different operations. A common PCM operation sequence begins as the PCM is moved along a set of rails that run in front of an oven battery to an assigned oven and align a coal charging system of the PCM with the oven. The pusher side oven door is removed from the oven using a door extractor from the coal charging system. The PCM is then moved to align a pusher ram of the PCM to the center of the oven. The pusher ram is energized, to push coke from the oven interior. The PCM is again moved away from the oven center to align the coal charging system with the oven center. Coal is delivered to the coal charging system of the PCM by a tripper conveyor. The coal charging system then charges the coal into the oven interior. In some systems, particulate matter entrained in hot gas emissions that escape from the oven face are captured by the PCM during the step of charging the coal. In such systems, the particulate matter is drawn into an emissions hood through the baghouse of a dust collector. The charging conveyor is then retracted from the oven. Finally, the door extractor of the PCM replaces and latches the pusher side oven door.
With reference to FIG. 1, PCM coal charging systems 10 have commonly included an elongated frame 12 that is mounted on the PCM (not depicted) and reciprocally movable, toward and away from the coke ovens. A planar charging head 14 is positioned at a free distal end of the elongated frame 12. A conveyor 16 is positioned within the elongated frame 12 and substantially extends along a length of the elongated frame 12. The charging head 14 is used, in a reciprocal motion, to generally level the coal that is deposited in the oven. However, with regard to FIGS. 2A, 3A, and 4A, the prior art coal charging systems tend to leave voids 16 at the sides of the coal bed, as shown in FIG. 2A, and hollow depressions in the surface of the coal bed. These voids limit the amount of coal that can be processed by the coke oven over a coking cycle time (coal processing rate), which generally reduces the amount of coke produced by the coke oven over the coking cycle (coke production rate). FIG. 2B depicts the manner in which an ideally charged, level coke bed would look.
The weight of coal charging system 10, which can include internal water cooling systems, can be 80,000 pounds or more. When charging system 10 is extended inside the oven during a charging operation, the coal charging system 10 deflects downwardly at its free distal end. This shortens the coal charge capacity. FIG. 3A indicates the drop in bed height caused by the deflections of the coal charging system 10. The plot depicted in FIG. 5 shows the coal bed profile along the oven length. The bed height drop, due to coal charging system deflection, is from five inches to eight inches between the pusher side to the coke side, depending upon the charge weight. As depicted, the effect of the deflection is more significant when less coal is charged into the oven. In general, coal charging system deflection can cause a coal volume loss of approximately one to two tons. FIG. 3B depicts the manner in which an ideally charged, level coke bed would look.
Despite the ill effect of coal charging system deflection, caused by its weight and cantilevered position, the coal charging system 10 provides little benefit in the way of coal bed densification. With reference to FIG. 4A, the coal charging system 10 provides minimal improvement to internal coal bed density, forming a first layer d1 and a second, less dense layer d2 at the bottom of the coal bed. Increasing the density of the coal bed can facilitate conductive heat transfer throughout the coal bed which is a component in determining oven cycle time and oven production capacity. FIG. 6 depicts a set of density measurements taken for an oven test using a prior art coal charging system 10. The line with diamond indicators shows the density on the coal bed surface. The line with the square indicators and the line with the triangular indicators show density twelve inches and twenty-four inches below the surface respectively. The data demonstrates that bed density drops more on the coke side. FIG. 4B depicts the manner in which an ideally charged, level coke bed would look, having relatively increased density layers D1 and D2.
Typical coking operations present coke ovens that coke an average of forty-seven tons of coal in a forty-eight hour period. Accordingly, such ovens are said to process coal at a rate of approximately 0.98 tons/hr, by previously known methods of oven charging and operation. Several factors contribute to the coal processing rate, including the constraints of draft, oven temperature (gas temperature and thermal reserve from the oven brick), and operating temperature limits of the oven sole flue, common tunnel, and associated components, such as Heat Recovery Steam Generators (HRSG). Accordingly, it has heretofore been difficult to attain coal processing rates that exceed 1.0 tons/hr.